Long data type NLS issue

I have a 9.2.0.6 DB that was created with AMERICAN US7ASCII character
set.
When our heavy PC client inserts into a LONG type column and the number
of characters is more than 2k we get
ORA-03106: fatal two-task communication protocol error

If we explicitly set NLS_LANG= AMERICAN_AMERICA.US7ASCII
Then the client works fine and we can insert up to 32k characters.

We want to do something at the server level (db level) because we can't
modify the client because we have 100s of clients that would need to be
modified.